Calcium Propionate is sold at the mill we buy from. It is used with most commonly with breads-it is a mould inhibitor so extends shelf life- although it can adversly affect products that contain baking powder.

Clio......glycerin will not stop moisture from forming on cakes. Cakes sweat under refrigeration......that's just how it is. When you talk about storing your cakes, are you talking about storing them decorated or undecorated? If they are just baked cake layers, wrap them well in plastic wrap and you should have no problems. If you are talking about a decorated (iced) cake, then put the cake in a box and wrap the box in plastic. This will reduce the sweating.

I make cup cakes (buns) they seem to sweat in a large plastic lunch box after a few hours / day. I make a batch of 50 as I have 3 kids and they love them. Handy for treat in lunch box. It would be a pain to have to make a smaller batch every 2nd day.